Fix initialization order issue causing missing asset errors in Sprockets

[camertron]

What are you trying to accomplish?

This PR should fix #2433, which describes an initialization order problem that causes Sprockets to raise missing asset errors.

What approach did you choose and why?

The issue includes a single-file reproduction, which was very useful in determining the fix. The problem boils down to initialization order. Both Sprockets and ViewComponent define a number of after_initialize blocks, which Rails invokes in the order they were added. The VC engine assumes the Sprockets railtie adds its "after initializers" first, but if VC's after initializers were added first, VC tries to read certain Sprockets config options which aren't yet set.

The fix is to wait until all after initializers have executed, at which point Sprockets should be fully set up. Fortunately Rails exposes the after_routes_loaded callback, which appears to fire after all initializers and after_initialize blocks.

[joelhawksley]

@jan-evermood @dark-panda @Paul-Bob would you mind testing #2566 in your apps before we land it?

[Paul-Bob]

gem "view_component", github: "ViewComponent/view_component", branch: "fix_sprockets_init_order"
gem "sprockets-rails"

Works for me ☝🏼

Thanks for looking into this, guys 🎉